Data from: Determinants of litter decomposition rates in a tropical forest: functional traits, phylogeny and ecological succession

Plant litter decomposition is one of the most important processes in terrestrial ecosystems, as it is a key factor in nutrient cycling. Decomposition rates depend on environmental factors, but also plant traits, as these determine the character of detritus. We measured litter decomposition rate for 57 common tree species displaying a variety of functional traits within four sites in primary and four sites in secondary tropical forest in Madang Province, Papua New Guinea. The phylogenetic relationships between these trees were also estimated using molecular data. The leaves collected from different tree species were dried for two days, placed into detritus bags and exposed to ambient conditions for two months. Nitrogen, carbon and ash content were assessed as quantitative traits and used together with a phylogenetic variance-covariance matrix as predictors of decomposition rate. The analysis of the tree species composition from 96 quadrats located along a successional gradient of swidden agriculture enabled us to determine successional preferences for individual species. Nitrogen content was the only functional trait measured to be significantly positively correlated with decomposition rate. Controlling for plant phylogeny did not influence our conclusions, but including phylogeny demonstrated that the mainly early successional family Euphorbiaceae is characterized by a particularly high decomposition rate. The acquisitive traits (high nitrogen content and low wood density) correlated with rapid decomposition were characteristic for early successional species. Decomposition rate thus decreased from early successional to primary forest species. However, the decomposition of leaves from the same species was significantly faster in primary than in secondary forest stands, very probably because the high humidity of primary forest environments keeps the decomposing material wetter.

植物枯落物分解是陆地生态系统的核心过程之一，亦是养分循环的关键调控因子。分解速率不仅受环境因子影响，同时由植物功能性状决定——后者直接塑造了枯落物的理化特征。本研究针对巴布亚新几内亚马当省的4处原始热带林与4处次生热带林样地内的57种常见乔木开展枯落物分解速率测定，所涉物种涵盖多样的功能性状类型。同时，我们基于分子数据推断了这些乔木的系统发育关系。我们将采集自不同乔木物种的叶片烘干两日，装入枯落物袋（detritus bags）后置于样地自然环境中，开展为期两个月的原位分解实验。我们测定了叶片的氮、碳与灰分含量作为定量功能性状，并结合系统发育方差-协方差矩阵，将二者共同作为分解速率的预测因子。通过对刀耕火种农业演替梯度上设置的96个样方（quadrats）内乔木物种组成的分析，明确了各物种的演替偏好。仅叶片氮含量这一功能性状与分解速率呈现显著正相关。在分析中纳入系统发育因素并未改变研究结论，但通过引入系统发育关系可见，以早演替类群为主的大戟科（Euphorbiaceae）具有极高的枯落物分解速率。与快速分解相关的获取型功能性状（高氮含量与低木材密度）是早演替乔木物种的典型特征。因此，枯落物分解速率从早演替物种向原始林物种逐渐降低。但同一物种的叶片枯落物在原始林样地中的分解速率显著快于次生林样地，这极有可能是因为原始林环境湿度更高，使得分解基质始终保持湿润状态。